The Billings Rimrocks: Sixty-Five Million Years of Seabed Over a City

The pale sandstone escarpment running along Billings's northern edge is roughly five hundred to eight hundred feet of exposed ancient seabed. About eighty million years ago, the interior of North America was covered by a shallow inland sea that stretched from the Arctic to the Gulf of Mexico. The Rimrocks are what remained when that sea retreated, compressed and lifted by the same geologic forces that built the Rocky Mountains. What you are looking at is ocean floor, left standing.

The caves and overhangs at the base of the escarpment contain Crow pictographs. The Apsaalooke used these sheltered sandstone surfaces for images whose purposes ranged from spiritual documentation to hunting records to territorial markers. The pictographs predate any Euro-American presence in the Yellowstone Valley by centuries. The Western Heritage Center in Billings holds documentation of these sites, though many of the specific locations are protected from broader publication to discourage vandalism.

When the Northern Pacific Railroad was planning its Yellowstone Valley route in the early eighteen eighties, the engineers who selected the Billings townsite in eighteen eighty-two were making a tactical decision. The Rimrocks made the position defensible. The Yellowstone River below made it navigable. The railroad placed its division headquarters at the base of an eighty-million-year-old natural wall and called the town Billings, after the railroad president who never visited.

The escarpment has not changed much since then. The city built up against it, highway overpasses threaded beneath it, and the caves where the pictographs are still there, waiting in the sandstone.